A communication system can be seen as a facility that enables communication sessions between two or more entities such as fixed or mobile communication devices, base stations, servers and/or other communication nodes. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how communication devices can access the communication system and how various aspects of communication shall be implemented between communicating devices. A communication can be carried on wired or wireless carriers. In a wireless communication system at least a part of the communication between at least two stations occurs over a wireless link.
Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). A wireless system can be divided into cells, and hence these are often referred to as cellular systems. A cell is provided by a base station. Cells can have different shapes and sizes. A cell can also be divided into sectors. Regardless of the shape and size of the cell providing access for a user, and whether the access is provided via a sector of a cell or a cell, such area can be called radio service area or access area. Neighbouring radio service areas typically overlap, and thus a communication in an area can listen to more than one base station.
A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically a communication device is used for enabling receiving and transmission of communications such as speech and data. In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. a base station of an access network and/or another user equipment. The communication device may access a carrier provided by a station, for example a base station, and transmit and/or receive communications on the carrier.
An example of communication systems attempting to satisfy the increased demands for capacity is an architecture that is being standardized by the 3rd Generation Partnership Project (3GPP). This system is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE aims to achieve various improvements, for example reduced latency, higher user data rates, improved system capacity and coverage, reduced cost for the operator and so on. A further development of the LTE is often referred to as LTE-Advanced. The various development stages of the 3GPP LTE specifications are referred to as releases.
In LTE-Advanced the network nodes can be wide area network nodes such as a macro eNode B (eNB) which may, for example, provide coverage for an entire cell. Alternatively in LTE-Advanced, network nodes can be small area network nodes such as Home eNBs (HeNB) or pico eNodeBs (pico-eNB). HeNBs may be configured to support local offload and may support any UE or UEs belonging to a closed subscriber group (CSG) or an open subscriber group (OSG). Pico eNBs can, for example, be configured to extend the range of a cell. In some instances a combination of wide area network nodes and small area network nodes can be deployed using the same frequency carriers (e.g. co-channel deployment).
In some cases a Macro-eNB and the HeNB share the entire bandwidth or a sub-carrier. This means that interference from HeNB having a closed subscriber group can be an issue. A user equipment visiting a cell of an HeNB and the visiting user equipment is not part of the closed subscriber group can be prevented from accessing the macro-eNB when close to the HeNB. Furthermore wide area dead zones can be cause by the downlink interference from the closed subscriber group nodes such as the HeNB. This means is can be impossible for the visiting user equipment to access the macro-eNB.
It is noted that the above discussed issues are not limited to any particular communication environment, but may occur in any appropriate communication system where muting of data transmissions may be provided.
Embodiments of the invention aim to address one or several of the above issues.
In accordance with an embodiment there is provided a method comprising: determining at least one first station and at least one second station have a relative timing difference; determining a muting schedule for the at least one first station for a plurality of sub-frames, wherein the muting schedule comprises at least two adjacent muted sub-frames; and initiating sending an indication of the muting schedule to the at least one first station and the at least one second station wherein information on one or more channels is transmitted from the at least one second station during the at least two adjacent muted sub-frames.
Preferably the muting schedule comprises an arrangement of muting sub-frames over a plurality of frames. More preferably the arrangement of muting sub-frames is different between each frame of the plurality of frames. Even more preferably the first station is muted for at least one sub-frame of sub-frames in the same relative position in each frame the muting schedule.
Preferably the muting schedule comprises an arrangement of muting sub-frames repeated every 3 or 4 frames.
Preferably the muting schedule comprises at least two unmuted sub-frames for the at least one first station to transmit information on the one or more control channels.
Preferably the at least one first station transmits substantially no data during the one or more muted sub-frames.
Preferably the information is sent on one or more control channels and the information comprises one or more of the following: information associated with a primary broadcast channel, information associated with a synchronisation channel, system information and paging information.
Preferably the method comprises modifying the muting schedule by switching one or more of the sub-frames between a muted stated and an unmuted state. More preferably the switching is performed after the indication of the muting schedule is sent to the at least one first station and the at least one second station. The modifying of the muting schedule may be carried out after determining the timing difference between the at least one first station and the at least one second station.
Preferably the muting schedule comprises not muting sub-frames during which the at least one first station performs an uplink HARQ procedure.
Preferably the at least one first station and the at least one second station operate on the same frequency carrier.
Preferably the determining when the first and second stations are unsynchronised and determining the muting schedule is based on information received from the at least one first station.
Preferably the first station is a home enhanced node B and the second station is a macro enhanced node B.
Preferably the muting schedule is predetermined and the predetermined muting schedule is stored in the memory of the first and second stations.
Preferably the initiating sending the indication comprises sending the indication to one or more mobile communication devices.
Preferably there is one or more muted sub-frames at one or both ends of consecutively muted sub-frames of one or more frames of the muting pattern.
In accordance with yet another embodiment there is provided a control apparatus comprising: a processor configured to determine at least one first station and at least one second station have a relative timing difference; determine a muting schedule for the at least one first station for a plurality of sub-frames, wherein the muting schedule comprises at least two adjacent muted sub-frames; and initiate sending an indication of the muting schedule to the at least one first station and the at least one second station wherein information on one or more channels is transmitted from the at least one second station during the at least two adjacent muted sub-frames.
In accordance with yet another embodiment there is provided a control apparatus comprising means for determining at least one first station and at least one second station have a relative timing difference; means for determining a muting schedule for the at least one first station for a plurality of sub-frames, wherein the muting schedule comprises at least two adjacent muted sub-frames; and means for initiating sending an indication of the muting schedule to the at least one first station and the at least one second station wherein information on one or more channels is transmitted from the at least one second station during the at least two adjacent muted sub-frames.
In accordance with yet another embodiment there is provided a control apparatus comprising: at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: determine at least one first station and at least one second station have a relative timing difference; determine a muting schedule for the at least one first station for a plurality of sub-frames, wherein the muting schedule comprises at least two adjacent muted sub-frames; and initiate sending an indication of the muting schedule to the at least one first station and the at least one second station wherein information on one or more channels is transmitted from the at least one second station during the at least two adjacent muted sub-frames.
A computer program comprising program code means adapted to perform the method may also be provided.
Various other aspects and further embodiments are also described in the following detailed description and in the attached claims.